Frame grid for electric discharge tubes



- March 29, 1960 w. LANGMAACK 2,930,923

FRAME can: FOR ELECTRIC DISCHARGE TUBES Filed April 24, 195

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INVENTOR WILHELM LAMMAAOK BY i 2 AGENT finited States FRAME GRID FOR ELECTRIC DISCHARGE TUBES Wilhelm Langmaaclr, Hambnrg-Lockstedt, Germany, as-

signor to North American Philips Company, Inc, New York, N.Y., a corporation of Delaware Application April 24, 1959, Serial No. 808,613

Claims priority, application Germany May 7, 1953 4 Claims. (Cl. 313-261) This invention relates to frame grids which are used in electric discharge tubes. In such frame grids, it is known to use spacers between the grid stays. These spacers bear along their full length on the discs of insulating material, in particular of mica, used to fix and support the electrode system. Owing to the metallic layers which are deposited from vapour on the mica discs during the degassing process and/or in operation, these surfaces become partly conductive. In addition, the spacers which rest upon the mica discs and are made from a metallic material, establish an electrically conductive connection betwen the grid stays and extend closely along the cathode, which is held by the same mica discs so that conductive bridges are produced over the mica discs which have been rendered conductive. Such insulation faults could be avoided by the provision of recesses in the spacers so that the latter, at least in the proximity of the cathode, are not in contact with the mica discs, or by the provision of recesses in the mica dics. While recesses in the spacers can only be produced laboriously, they cannot be provided at all in the mica discs owing to the small spacing between the grid and the cathode.

It is an object of the present invention to provide a frame grid for electric discharge tubes in which the spacers interposed between the grid stays are secured thereto so that after mounting of the electrode system, they are inclined relatively to the disc-shaped insulating and supporting members, which preferably are made of mica, and are substantially in point contact only with these members.

The formation of conductive bridges between grid and cathode is impeded by the construction in accordance with the invention, since each spacer bears on a mica disc at one point only. Hence leakage currents between grid and cathode must travel the entire distance between the grid stays and the cathode over the mica discs.

In order that the invention may readily be carried out,

Gee

pair on either side of each stay end 3. The stay ends 3 pass through apertures in two mica discs 5, which support not only the entire grid 1 but also a cathode 6 against a tube envelope which is not shown for the sake of simplicity. The grid 1 is made up from grid wires 7 which are wound on the grid stays 2 between the spacers 4.

Each spacer 4 engages the mica disc 5 concerned substantially at a single point only since they are inclined to these mica discs 5, for example at least approximately at an angle corresponding to the pitch of the grid turns. All the spacers may be arranged parallel to each other, however, the two spacers which are arranged opposite each other at a grid end on both sides of the grid stays 2 may be secured to these stays 2 at opposite angles.

Fig. 2 shows that the distance at which the spacers 4 extend along the cathode 6 is minute so that there is a great likelihood of the formation of conducting bridges between the spacers 4 and the cathode 6 owing to metal layers being deposited from vapour, if the spacers 4 engage the mica discs 5 along their full length, as was usual hitherto. Since, however, according to the invention the spacers 4 do not contact the mica discs 5 'at the area at which they extend on both sides past the cathode 6, the formation of conducting bridges between grid and cathode is materially impeded.

What is claimed is:

1. A frame grid for electric discharge tubes, comprising a plurality of spaced grid-stay members about which the turns of the grid are Wound with a given pitch, a pair of disc-shaped insulating support-members through which the grid-stay members extend, and a plurality of grid spacer members inclined relative to and in substantial point contact with the disc-shaped support members.

2. A frame grid as claimed in claim 1, in which the spacer members are inclined at an angle which corresponds at least approximately to the pitch of the grid turns.

3. A frame grid as claimed in claim 1, in which the spacer members are arranged opposite each other at a grid end, are secured to the grid stays at opposite angles.

4. A frame grid as claimed in claim 1 in which the support members are made of mica.

No references cited. 

